Process for producing aliphatic oligocarbonate diols

ABSTRACT

The present invention relates to a process for producing an aliphatic oligocarbonate diol comprising a) reacting an aliphatic diol with dimethyl carbonate at an elevated pressure in a reaction mixture, and b) subsequently removing unreacted methanol and dimethyl carbonate under a reduced pressure to uncap the terminal OH groups.

FIELD OF THE INVENTION

The present invention relates to a new process for producing aliphaticoligocarbonate diols by the transesterification of aliphatic diols withdimethyl carbonate (DMC) under elevated pressure. The process accordingto the invention also makes it possible to produce aliphaticoligocarbonate diols on a large industrial scale and with a highspace-time yield (STY) from readily available DMC.

BACKGROUND OF THE INVENTION

Aliphatic oligocarbonate diols are important precursors for theproduction of plastics, lacquers and adhesives, for example. They arereacted with isocyanates, epoxides, (cyclic) esters, acids or acidanhydrides, for example. They can be produced from aliphatic diols bythe reaction thereof with phosgene (e.g. DE-A 1 595 446), esters ofbis-chlorocarbonic acid (e.g. DE-A 0 857 948), diaryl carbonates (e.g.DE-A 1 915 908), cyclic carbonates (e.g. DE-A 2 523 352: ethylenecarbonate) or dialkyl carbonates (e.g. DE-A 2 555 805).

Of the carbonate sources, diphenyl carbonate (DPC), which is a diarylcarbonate, is particularly important, since aliphatic oligocarbonatediols of particularly high quality can be produced from DPC (e.g. U.S.Pat. No. 3,544,524, EP-A 0 292 772). In contrast to all other carbonatesources, DPC reacts quantitatively with aliphatic OH functions, so thatafter removing the phenol which is formed, all the terminal OH groups ofthe oligocarbonate diol are available for reaction, e.g. with isocyanategroups. Moreover, only very low concentrations of a soluble catalyst arerequired, so that the latter can remain in the product.

Processes based on DPC have the following disadvantages, however:

Only about 13% by weight of the DPC remains as CO groups in theoligocarbonate; the remainder is distilled off as phenol. Asignificantly higher proportion of dialkyl carbonates remains in theoligocarbonate, depending on the alkyl radical concerned. Thus about 31%by weight of dimethyl carbonate (DMC) is available as CO for theoligocarbonate, since the methanol which is distilled off has amolecular weight which is considerably lower than that of phenol.

Because high-boiling phenol (normal boiling point: 182° C.) has to beseparated from the reaction mixture, it is only diols with a boilingpoint considerably higher than 182° C. which can be used in thereaction, in order to prevent unwanted removal of the diol bydistillation.

Due to their ease of production, dialkyl carbonates, particularlydimethyl carbonate (DMC), are distinguished as starting materials bybeing more readily available. For example, DMC can be obtained by directsynthesis from MeOH and CO (e.g. EP-A 0 534 454, DE-A 19 510 909).

Numerous publications (e.g. U.S. Pat. Nos. 2,210,817, 2,787,632, EP-A364 052) relate to the reaction of dialkyl carbonates with aliphaticdiols:

In the prior art, aliphatic diols are placed in a vessel together with acatalyst and the dialkyl carbonate (e.g. diethyl carbonate, dibutylcarbonate, diallyl carbonate), and the resulting alcohol (e.g. ethanol,butanol, allyl alcohol) is distilled off from the reaction vessel via acolumn. In the column, the higher boiling, dialkyl carbonate isseparated from the lower boiling alcohol and is recycled to the reactionmixture.

Despite its ready availability, the use of dimethyl carbonate (DMC) forthe production of aliphatic oligocarbonate diols has only recentlybecome known (e.g. U.S. Pat. No. 5,171,830, EP-A 798 327, EP-A 0 798328, DE-A 198 29 593).

EP-A 0 798 328 describes the reaction of the corresponding diolcomponent with DMC with distillation of the azeotrope under normalpressure. Uncapping is subsequently effected by vacuum distillation,wherein degrees of utilization of the terminal OH groups of about 98%are achieved under very drastic vacuum conditions (1 torr, about 1.3mbar) (EP-A 0 798 328: Table 1).

EP-A 0 798 327 describes a corresponding two-step process in which adiol is first reacted with an excess of DMC, with distillation of theazeotrope under normal pressure, to form an oligocarbonate, the terminalOH groups of which are present as methoxycarbonyl terminal groups andare completely inaccessible. After removing the catalyst anddistillation of the excess DMC under vacuum (65 torr, 86 mbar) theoligocarbonate diol is obtained in a second step by the addition offurther amounts of the diol and of a solvent (e.g. toluene) as anentraining agent for the methanol formed. The remainder of the solventthen has to be distilled off under vacuum (50 torr, 67 mbar). Thedisadvantages of this process are the cost of conducting it by the useof a solvent, and the repeated distillation which is required, as wellas the very high consumption of DMC.

DE-A 198 29 593 teaches the reaction of a diol with DMC, with themethanol formed being distilled off under normal pressure. Apart from asingle mention of the word “azeotrope” in the table headed “Processdiagram of the process according to the invention”, no consideration isgiven there to the overall problem of the azeotrope. It can becalculated from the examples that DMC is used in excess and isazeotropically distilled off. About 27.8% by weight of the DMC used islost.

According to U.S. Pat. No. 5,171,830, a diol is first heated with DMCand volatile constituents are then (azeotropically) distilled off. Aftervacuum distillation under drastic conditions (1 torr, 1.3 mbar), take-upof the product in chloroform, precipitation of the product with methanoland drying the product, an oligocarbonate diol is obtained in a yield of55% by weight theoretical (loc. cit., Example 6). The degree ofutilization of the terminal OH groups and the azeotrope problems are notconsidered in detail. Although U.S. Pat. No. 5,171,830 mentions, incolumn 5, lines 24 to 26, that the process can be conducted undervacuum, at normal pressure and at elevated pressures, and therefore canbe conducted under all pressures, the particular preferences regardingthe conditions of pressure employed cannot be identified. It is only aprocedure which employs reduced pressure for the removal of volatileconstituents which is mentioned.

Therefore, in the above publications, which were known hitherto, thereis no description of a process, which is simple to carry outindustrially, for the reaction of DMC with aliphatic diols to formoligocarbonate diols with high space-time yields and with high degreesof utilization of the terminal OH groups.

It is an object of the present invention to provide a simple, productiveprocess, which can also be carried out on a large industrial scale, andwhich enables oligocarbonate diols to be produced by thetransesterification of aliphatic diols with dimethyl carbonate,optionally with the use of an amount of catalyst which is low enough forthe latter to remain in the product after completion of the reaction,with good space-time yields and with a high degree of uncapping of theterminal OH groups, in simple apparatuses.

It has now been found that the production of aliphatic oligocarbonatediols by the reaction of aliphatic diols with dimethyl carbonate, withthe reaction optionally being accelerated by catalysts, at elevatedpressure, results in a high space-time yield. In order to complete thereaction and in order to uncap the terminal OH groups (render the latterutilizable), the final residues of methanol and traces of dimethylcarbonate are removed from the product under reduced pressure,optionally with the introduction of inert gas.

SUMMARY OF THE INVENTION

The invention relates to a process for producing an aliphaticoligocarbonate diol comprising a) reacting an aliphatic diol withdimethyl carbonate at an elevated pressure, and b) subsequently removingunreacted methanol and dimethyl carbonate under a reduced pressure touncap the terminal OH groups.

The present invention also relates to a process of making a polymericmaterial comprising reacting the oligocarbonate diol.

DETAILED DESCRIPTION OF THE INVENTION

The process according to the invention is conducted under elevatedpressure, preferably under a pressure of 1.5 to 100 bar and morepreferably under a pressure of 3 to 16 bar and—depending on the pressureemployed—at temperatures from 100 to 300° C., preferably at temperaturesfrom 160 to 240° C.

At a constant catalyst concentration, an elevated pressure results in abetter conversion of DMC and in a shortening of the reaction times,which has a positive effect on the space-time yield.

Completion of the reaction and uncapping of the terminal OH groups(rendering the latter utilizable) are achieved by removing the finalresidues of methanol and traces of dimethyl carbonate under reducedpressure. In one preferred embodiment, completion the reaction anduncapping of the terminal OH groups (rendering the latter utilizable)are effected by introducing an inert gas (e.g. N₂) into theoligocarbonate diol under what is only a slight vacuum of about 150mbar. The gas bubbles are saturated with methanol or DMC and themethanol is thus almost completely expelled from the reaction batch. Bystripping with an inert gas to remove methanol, the equilibrium can befurther displaced in favour of the product, the transesterification iscompleted and the terminal groups are thus rendered utilizable. Thequality of the resulting oligocarbonate diol can be raised to the levelof f DPC-based oligocarbonate diols, and the degree of uncapping of theterminal OH groups increases to more than 98%, preferably to 99.0 to99.95%, most preferably to 99.5 to 99.9%.

Gas bubbles can be produced by introducing inert gases such as nitrogen,noble gases such as argon, or methane, ethane, propane, butane, dimethylether, dry natural gas or dry hydrogen into the reactor, wherein part ofthe gas stream which leaves the oligocarbonate and which containsmethanol and dimethyl carbonate can be rerouted to the reaction of theoligocarbonate for completion of the reaction. Nitrogen is preferablyused. Air can be used if products of low standard with respect to colorare to be made.

Gas bubbles can also be produced by introducing inert, low boilingliquids such as pentane, cyclopentane, hexane, cyclohexane, petroleumether, diethyl ether or methyl tert-butyl ether, etc., wherein thesesubstances can be introduced in liquid or gaseous form, and part of thegas stream which leaves the oligocarbonate and which contains methanoland dimethyl carbonate can be recycled to the oligocarbonate forsaturation.

The substances for producing gas bubbles can be introduced into theoligocarbonate via simple immersion tubes, preferably by means ofannular nozzles or gasification agitators. The degree of utilization ofthe terminal OH groups which is achieved depends on the duration ofuncapping, and on the amount, size and distribution of the gas bubbles:with increasing duration of uncapping and better distribution (e.g.better distribution and a larger phase boundary, due to a larger numberof smaller gas bubbles when the latter are introduced via a gasificationagitator) the degree of utilization is better. When introducingnitrogen, for example (e.g. at 150 mbar, 8 kettle volumina/hour), usinga gasification agitator, a degree of utilization of about 99% isachieved after one hour, and a degree of utilization of about 99.8% isachieved after about 5 to 10 hours.

Uncapping, optionally assisted by the introduction of inert gas bubblesinto the reaction mixture, is conducted at temperatures from 160° C. to250° C., preferably at temperatures from 200° C. to 240° C., and underpressures from 1 to 1000 mbar, preferably under pressures from 30 to 400mbar, most preferably under pressures from 70 to 200 mbar.

During the production of oligocarbonate diols, DMC is distilled offduring the production process. The amount of DMC which has been removedby distillation from the reaction batch is determined by determining theDMC content of the distillate. This missing amount has to be made upbefore stripping off the methanol with inert gases under vacuum to makethe terminal groups utilizable. A mixture of DMC and methanol formsagain. The DMC which is lost by the stripping can be added again, andanother part is distilled off again. With each addition the amount ofDMC which is distilled off becomes less, and the desired stoichiometryis thereby approached.

This costly procedure can be simplified by combining the individualaddition steps. The amounts of DMC which were distilled off can bemeasured in previous batches made with individual addition steps. It istherefore possible subsequently to add the complete amount of DMCtogether in a single step.

Thus the total amount of DMC required, namely the sum of the amountwhich is predetermined by the stoichiometry of the desired producttogether with the amount of DMC which is distilled off whilst thereaction is conducted, is added directly in the first step.

During the distillation of the methanol and the uncapping of the OHterminal groups at the end of the reaction when inert gas bubbles areintroduced, a small amount of DMC is lost. This amount has to be takeninto account beforehand by the addition of DMC. The requisite amount canbe determined from previous batches, based on experience.

In one preferred process variant, an excess of DMC is added at the startof the reaction which is calculated so that after distilling off theazeotrope and after uncapping, a product is formed which comprises thecomplete functionality of the terminal OH groups, but which has a degreeof polymerisation which is too high. A correction is then made by addinga further amount of the diol component and by conducting a brieftransesterification step again. The correction amount can firstly bedetermined via the mass balance—by determining the amount of DMC in allthe distillates and making a comparison with the total amount added—orfrom a measurable property (e.g. OH number, viscosity, average molecularweight, etc.) of the product, the degree of polymerisation of which istoo high. Renewed uncapping is not necessary after this correction,since all the terminal OH groups are already freely available before thecorrection, and the addition of the diol components does not result inrenewed capping.

Correction by the addition of DMC, after uncapping by gasification withan inert gas for a product which contains too little DMC, results inrenewed capping.

According to the invention, the diols and optionally the catalysts whichare present, are placed in a reaction vessel, the reactor is heated, thepressure is applied and DMC is subsequently metered in.

In one embodiment of the invention the process according to theinvention therefore comprises the following steps:

Placing the diol components and optionally the catalyst in a vessel.

Heating and application of pressure.

Introduction and reaction of the DMC. The amount of DMC is calculated sothat after removal by distillation in all steps (addition of DMC anduncapping) it is just the requisite amount of DMC or alternatively aslight excess thereof which remains in the reaction solution. Meteredaddition can be conducted according to two different strategies:

a) The complete amount of DMC is metered in rapidly in one step. As aconsequence, the STY is optimised. A DMC-methanol mixture is distilledoff which has a relatively high DMC content (e.g. the azeotrope), whichis considerably less than that obtained in a pressureless procedure.

b) The DMC is metered in in two partial steps. The DMC is first meteredin slowly, so that DMC-methanol mixtures with low DMC contents aredistilled off. Not until a later point in time, when the DMC content inthe distillate significantly increases, even at the same slow rate ofaddition, is the DMC rapidly metered in, so that a distillate with ahigh DMC content (e.g. a DMC-methanol azeotrope) is formed.

Procedure b) results in better utilization of the DMC and in an inferiorSTY.

Uncapping: rendering the terminal OH groups utilizable by extracting thefinal residues of methanol and DMC under reduced pressure, optionally bythe production of gas bubbles (e.g. by the introduction of inert gasessuch as N₂).

Correction: correction of the stoichiometry, if necessary, by addingfurther amounts of the diol components and another brieftransesterification.

It is also possible, of course, for the process according to theinvention to be conducted with an excess of diol. In a procedure of thistype, a correction subsequently has to be made wit DMC. This thenresults in a repeated uncapping step.

In a further embodiment of the invention up to 100%, preferably up to70%, more preferably up to 50% and most preferably up to 30% of the DMCis placed in the reaction vessel at the start, together with the diolsand the catalyst which is optionally present. The reactor issubsequently closed, heated and pressure is applied. All the distillateis first recirculated to the reactor. The DMC content can be determinedby taking a sample from the distillate stream. Depending on theoptimisation target (DMC yield or STY), a reflux ratio of 100% can beemployed until a minimal DMC content in the distillate is achieved, or adefined time is fixed at which a changeover is made to distillation (aDMC/methanol mixture is distilled off). The residual DMC is subsequentlymetered in, uncapped, and any necessary correction to the stoichiometryis made by adding further amounts of the diol components and by arenewed, brief transesterification.

Suitable aliphatic diols preferably have 3 to 20 C atoms in their chain.Examples include 1,7-heptanediol, 1,8-octanediol, 1,6-hexanediol,1,5-pentanediol, 1,4-butanediol, 1,3-butanediol, 1,3-propanediol,2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2-methylpentanediol,2,2,4-trimethyl-1,6-hexanediol, 3,3,5-trimethyl-1,6-hexanediol,2,3,5-trimethyl-1,6-hexanediol, cyclohexane-dimethanol, and others, aswell as mixtures of different diols.

Addition products of diols with lactones (ester diols) can also be used,such as caprolactone, valerolactone etc., as can mixtures of diols withlactones, wherein it is not necessary initially to transesterify alactone and diols.

Moreover, addition products of diols with dicarboxylic acids can also beused, such as: adipic acid, glutaric acid, succinic acid, malonic acid,etc., or esters of dicarboxylic acids and also mixtures of diols withdicarboxylic acids or with esters of dicarboxylic acids, wherein it isnot necessary initially to transesterify a dicarboxylic acid and diols.

Polyether polyols can also be used, such as polyethylene glycol,polypropylene glycol and polybutylene glycol, as can polyether polyolswhich are obtained by the copolymerisation of ethylene oxide andpropylene oxide for example, or polytetramethylene glycol which isobtained by the ring-opening polymerisation of tetrahydrofuran (THF).

Mixtures of different diols, lactones and dicarboxylic acids can beused.

1,6-hexanediol, 1,5-pentanediol and/or mixtures of 1,6-hexanediol andcaprolactone are preferably used in the process according to theinvention.

ε-caprolactone esters are preferably formed in situ, without priorreaction, from the raw materials during the production of oligocarbonatediol.

In principle, all soluble catalysts which are known fortransesterification reactions can optionally be used as catalysts(homogeneous catalysis), and heterogeneous transesterification catalystscan also be used. The process according to the invention is preferablyconducted in the presence of a catalyst.

Hydroxides, oxides, metal alcoholates, carbonates and organometalliccompounds of metals of main groups I, II, III and IV of the periodictable of the elements, of subgroups III and IV, and elements from therare earth group, particularly compounds of Ti, Zr, Pb, Sn and Sb, areparticularly suitable for the process according to the invention.

Suitable examples include: LiOH, Li₂CO₃, K₂CO₃, KOH, NaOH, KOMe, NaOMe,MeOMgOAc, CaO, BaO, KOt-Bu, TiCl₄, titanium tetraalcoholates orterephthalates, zirconium tetraalcoholates, tin octoate, dibutyltindilaurate, dibutyltin, bistributyltin oxide, tin oxalate, lead stearate,antimony trioxide, zirconium tetraisopropylate, etc.

Aromatic nitrogen heterocycles can also be used in the process accordingto the invention, as can tertiary amines corresponding to R₁R₂R₃N, whereR₁₋₃ independently represents a C₁-C₃₀ hydroxyalkyl, a C₄-C₁₀ aryl or aC₁-C₃₀ alkyl, particularly trimethylamine, triethylamine, tributylamine,N,N-dimethylcyclohexylamine, N,N-dimethyl-ethanolamine,1,8-diaza-bicyclo-(5.4.0)undec-7-ene, 1,4-diazabicyclo-(2.2.2)octane,1,2-bis(N,N-dimethyl-amino)-ethane, 1,3-bis(N-dimethyl-amino)propane andpyridine.

Alcoholates and hydroxides of sodium and potassium (NaOH, KOH, KOMe,NaOMe), alcoholates of titanium, tin or zirconium (e.g. Ti(OPr)₄), aswell as organotin compounds are preferably used, wherein titanium, tinand zirconium tetraalcoholates are preferably used with diols whichcontain ester functions or with mixtures of diols with lactones.

In the process according to the invention, the homogeneous catalyst isused in concentrations (expressed as percent by weight of metal withrespect to the aliphatic diol used) of up to 1000 ppm (0.1%), preferablybetween 1 ppm and 500 ppm (0.05%), most preferably between 5 ppm and 100ppm (0.01%). After the reaction is complete, the catalyst can be left inthe product, or can be separated, neutralized or masked. The catalyst ispreferably left in the product.

The molecular weight of the oligocarbonate diols produced by the processaccording to the invention can be adjusted via the molar ratio of diolto DMC, wherein the molar ratio of diol/DMC can range between 1.01 and2.0, preferably between 1.02 and 1.8, and most preferably between 1.05and 1.6. The aforementioned ratio, of course, describes thestoichiometry of the product, i.e., the effective ratio of diol to DMCafter distilling off the DMC-methanol mixtures. The amounts of DMC whichare used in each case are correspondingly larger due to the azeotropicdistillation of the DMC. The calculated number-average molecular weightsof the oligocarbonate diols produced by the process according to theinvention then range, e.g. when 1,6-hexanediol is used as the diolcomponent, between 260 and 15,000 g/mol, preferably between 300 and 7300g/mol, most preferably between 350 and 3000 g/mol. If a diol of higheror lower molecular weight is used, the molecular weights of theoligocarbonate diols produced according to the invention arecorrespondingly higher or lower.

The process according to the invention makes it possible to produceoligocarbonate diols of formula HO—R₁—[—O—CO—O—R₁—]_(n)—OH which havecarbon numbers from 7 to 1300, preferably from 9 to 600, most preferablyfrom 11 to 300, in which R₁ is the symbol for aliphatic diols with 3 to50 carbon atoms, preferably 4 to 40, and more preferably from 4 to 20carbon atoms.

The diols can additionally contain ester, ether, amide and/or nitrilefunctions. Diols or diols with ester functions are preferred, such asthose which are obtained by the use of caprolactone and 1,6-hexanediol.If two or more diol components are used (e.g. mixtures of differentdiols or mixtures of diols with lactones), two adjacent R₁ groups in amolecule can definitely be different from each other (randomdistribution).

The process according to the invention enables high qualityoligocarbonate diols to be produced from DMC with good space-time yieldsand with a low degree of capping of their terminal OH groups.

The oligocarbonate diols which are produced by the process according tothe invention can be used, for example, for the production of plasticspolymers, fibres, coatings, lacquers and adhesives, e.g. by reactionwith isocyanates, or for the production of epoxides, (cyclic) esters,acids or acid anhydrides. They can be used as binder vehicles, bindervehicle constituents and/or as reactive thinners in polyurethanecoatings. They are suitable as components of moisture-hardeningcoatings, or as binder vehicles or binder vehicle constituents insolvent-containing or aqueous polyurethane coatings. They can also beused as building blocks for the synthesis of polyurethane prepolymerswhich contain free NCO groups, or in polyurethane dispersions.

The oligocarbonate diols which are produced by the process according tothe invention can also be used for the production of syntheticthermoplastic materials such as aliphatic and/or aromaticpolycarbonates, thermoplastic polyurethanes, etc.

The invention is further illustrated but is not intended to be limitedby the following examples in which all parts and percentages are byweight unless otherwise specified.

EXAMPLES

Examples 1-6 according to the invention are examples of some synthesisof oligocarbonate diols with an OH number of 53-58 mg KOH/g and aresidual methanol content of <10 ppm, produced by a pressurizedprocedure. The comparison example demonstrates a synthesis using apressureless procedure.

Example 1

2316 kg 1,6-hexanediol, 2237 kg ε-caprolactone and 0.54 kg titaniumtetraisopropylate were placed in a reaction vessel fitted with across-arm agitator. The pressure was increased to 5.2 bar (abs.) withnitrogen. The batch was subsequently heated to 205° C. over 3 hours. Thepressure was held constant at 5.2 bar by means of a pressure controlsystem. After the desired temperature was reached, 800 kg dimethylcarbonate were added over 4 hours via an immersion tube (about 200kg/hour). At the same time, a distillate with a DMC content of about 11%was distilled off into a receiver. Thereafter, the temperature wasreduced to 195° C., and a further 1200 kg dimethyl carbonate weremetered in over 12 hours (about 100 kg/hour). After the metered additionof 400 kg of the 1200 kg, the DMC content in the distillate was about15%, after the metered addition of 800 kg it was about 24%, and at theend of the metered addition it was about 29%. After 4 hours of furtherreaction, the temperature was increased to 200° C. and the pressure wasreduced over 7 hours from 5.2 bar to 100 mbar. 10 Nm³ nitrogen wereintroduced via an immersed inlet tube. The residual methanol wasremoved. After 4 hours, the OH number was 42.5 mg KOH/g and theviscosity was 25,464 mPa.s. A further 80 kg 1,6-hexanediol were added.After a further 9 hours, the OH number was 50.0 mg KOH/g and theviscosity was 20,748 mPa.s. A further 50 kg 1,6-hexanediol were added.After a further 5 hours, the OH number was 57.9 mg KOH/g and theviscosity was 14,513 mPa.s. The residual methanol content was <10 ppm.The total run time was about 48 hours.

Example 2

2316 kg 1,6-hexanediol, 2237 kg ε-caprolactone, 0.54 kg titaniumtetraisopropylate and 1000 g dimethyl carbonate were placed in areaction vessel fitted with a cross-arm agitator. The pressure wasincreased to 5.2 bar (abs.) with nitrogen. The batch was subsequentlyheated to 180° C. over 2 hours. The pressure was held constant at 5.2bar by means of a pressure control system. A slight reflux occurred, theliquid from which was returned to the vessel. 1 hour after reaching 180°C., the dimethyl carbonate content in the reflux was about 17%, anddecreased to about 12.5% after a further 5 hours.

The apparatus was changed over to effect distillation into a receiverand the batch was heated to 194° C. Methanol with a DMC content of about12% distilled over. After about 4 hours, the distillation was complete.

1000 kg dimethyl carbonate were added at a rate of 250 kg/hour via animmersion tube, and a methanol/DMC azeotrope with a DMC content of about20-25% was distilled off. The batch was subsequently heated to 200° C.over 1 hour. After stirring for a further 2 hours, the pressure wasreduced to 200 mbar over 7 hours. 8 Nm³ nitrogen were then introducedvia an immersed inlet tube and the residual methanol was removed. After6 hours, the OH number was 43.2 mg KOH/g and the viscosity was 23,371mPa.s. 74 kg 1,6-hexanediol were then added. After a further 6 hours,the OH number was 48.8 mg KOH/g and the viscosity was 20,001 mPa.s. Theresidual methanol content was 20 ppm. A further 55 kg 1,6-hexanediolwere added. After a further reaction time of 6 hours, the OH number was56.5 mg KOH/g and the viscosity was 15,500 mPa.s. The residual methanolcontent was <10 ppm. The total run time was about 45 hours.

Example 3

A 200 liter stirred vessel with a paddle mixer was fitted with a packedcolumn of length 2.5 m (o.d. 11 cm, filled with Pall packings), acondenser and a 100 liter receiver. The distillate caught in thereceiver could be recycled to the reactor via a bottom pump and basalflange.

62,353 kg adipol, 60,226 kg ε-caprolactone, 12 g titaniumtetraisopropylate and 23.5 kg DMC were placed in the reactor. Afterrendering the reactor atmosphere inert by evacuating it twice to 300mbar and subsequently filling it with nitrogen, the batch was heated to80° C. over 1 hour and homogenized. A pressure of 5.2 bar was set byfilling with nitrogen under pressure, and the pressure was held constantby means of a pressure control system. The batch was subsequently heatedto 194° C. over 2 hours, and the temperature was held constant for 2hours.

A further 33.49 kg DMC were metered into the stirred vessel over 2 hoursat 194° C. After adding the DMC, the batch was heated to 196° C. over 30minutes and this temperature was held for 5 hours. The batch wassubsequently heated to 200° C. over 30 minutes and the entireDMC/methanol mixture (31 kg, with a DMC content of 25.7%) was distilledoff over 2 hours. The pressure was then reduced to 100 mbar over 1 hourand nitrogen was passed through the batch. After vacuum distillation for7 hours at 100 mbar and 200° C. whilst passing nitrogen through thebatch, an OH number of 60.3 mg KOH/g and a viscosity of 8,667 mPa.s (23°C.) were obtained, after a further 2 hours the OH number was 55.8 andthe viscosity was 13,099 mPa.s, and after a further 7 hours the OHnumber was 53.7 and the viscosity was 15,794 mPa.s.

The run time was 40 hours and the DMC content in the distillate was25.7%.

Example 4

9,267 kg 1,6-hexanediol and 0.13 g tetraisopropyl titanate were placedin a 20 liter pressure autoclave fitted with a cross-arm agitator, acolumn and a downstream condenser and receiver. After rendering thereactor atmosphere inert by evacuating it twice to 300 mbar andsubsequently filling it with N₂, the pressure in the reactor and theperipheral parts thereof (column, condenser, receiver) was set to 5.2bar with N₂. The batch was subsequently heated to 197° C. and 9.63 kgDMC was metered into the reactor over 6 hours. After the meteredaddition phase, the batch was heated to 200° C. and was distilled for 2hours at this temperature. 6.17 kg of a distillate with a DMC content of25.1% were obtained. The pressure was reduced to 100 mbar and nitrogenwas passed through the batch. After 9 hours, an OH number of 159 mgKOH/g was obtained. The pressure was set to 5.2 bar again and 1 kg DMCwere metered in over 1 hour. After the metered addition, the batch wasfirst stirred for 2 hours, and the pressure was then reduced to 100 mbaragain and the batch was distilled whilst passing nitrogen through it.After a further vacuum distillation for 18 hours at 100 mbar and 200°C., the OH number was 65.5 mg KOH/g. The pressure was increased to 5.2bar, 96 g DMC were metered in, and the batch was stirred for 2 hours,depressurized, evacuated to 100 mbar and distilled whilst passingnitrogen through it. After 19 hours, a product was finally obtainedwhich had an OH number of 56.0 mg KOH/g and a viscosity of 1,699 mPa.s(75° C.).

Example 5

Reactor: a 20 liter Hagemann reactor fitted with a cross-arm agitator, acolumn and a downstream condenser and receiver. Dimethyl carbonate wasmetered directly into the reactor via a diaphragm pump (not immersed).

6.68 kg 1,6-hexanediol (0.057 kmol), 6.45 kg ε-caprolactone (0.057 kmol)and 1 g tetraisopropyl titanate were placed in the reactor. Afterrendering the reactor atmosphere inert by evacuating it twice to 300mbar and subsequently filling it with nitrogen, the batch was firstheated to 80° C. over 1 hour and was then heated to 194° C. over 1 hour.

At 194° C., 6.14 kg dimethyl carbonate (0.068 kmol) were metered in overabout 5 hours. After the metered addition was complete, the batch washeld for 4 hours at 196° C. and the temperature was then increased to200° C. After 2 hours at 200° C. the reactor was depressurized to normalpressure and the distillate which had passed over (2.9 kg) was removedfrom the receiver. After removing the distillate, the pressure wasreduced to 100 mbar and nitrogen was passed through the batch. After 6hours, a viscosity of 42,135 mPa.s and an OH number of 29.8 mg KOH/gwere obtained. In order to achieve the desired OH number of 53-58 mgKOH/g, 0.413 kg 1,6-hexanediol were subsequently added, and the batchwas held for a further 6 hours at 200° C. and at a pressure of 100 mbarwhilst passing nitrogen through it. An OH number of 45.8 mg KOH/g and aviscosity 21,725 mPa.s were obtained. A further 0.150 kg adipol wasadded. After a further 8 hours, a viscosity of 18,330 mPa.s and an OHnumber of 56.8 mg KOH/g were obtained.

The total reaction time was about 36 hours.

Example 6

9270 kg 1,6-hexanediol, 8950 kg ε-caprolactone were placed at 100° C. ina reaction vessel fitted with a cross-arm agitator and a condenser. 1.5kg titanium tetraisopropylate were added. The pressure was increased to5.2 bar (abs.) with nitrogen. The batch was subsequently heated to 200°C. After the desired temperature was reached, 7300 kg dimethyl carbonatewere equally added over 15 hours. At the same time the methanol formedwas distilled off as a distillate with a DMC content of about 15-19% byweight. Thereafter, the temperature was reduced to 180° C., and thepressure was reduced over 3 hours to ambient pressure. The pressure isfurther reduced over 12 hours to 60 mbar. 2 Nm³/h nitrogen wereintroduced via an immersed inlet tube to take out residual methanol. Thevacuum was further reduced to 20 mbar. After a further 24 hours at 180°C., the residual non-OH-endgroups (especially methylcarbonate groups)were less than 5 mol %. The reactor was cooled to 100° C., brought toambient pressure and the product filtered. It yielded 20000 kg of aclear, colorless noncrystralline resin with an OH number of 56 mg KOH/gand a viscosity of 15,000 mPa.s at 23° C.

Comparison Example

Production of the product from Example 5 by a pressureless procedure

Reactor: A 20 liter Hagemann reactor fitted with across-arm agitator, acolumn and a downstream condenser and receiver. Dimethyl carbonate wasmetered directly into the reactor via a diaphragm pump (not immersed).

6.68 kg 1,6-hexanediol (0.057 kmol), 6.45 kg ε-caprolactone (0.057 kmol)and 1 g tetraisopropyl titanate were placed in the reactor. Afterrendering the reactor atmosphere inert by evacuating it twice to 300mbar and subsequently filling it with N₂, the batch was first heated to80° C. over 1 hour and was then heated to 140° C. over a further 1 hour.At 140° C., 6.14 kg dimethyl carbonate (0.068 kmol) were metered in sothat the column top temperature did not exceed 67° C. The time ofmetered addition was about 24 hours at a column bottom temperature of140 to 182° C. After the metered addition was complete, the temperaturewas increased to 200° C. over about 1 hour. 4 hours after reaching 200°C., an OH number of 85.7 mg KOH/g was determined. The batch was cooledto 140° C. and was corrected with 0.357 kg of pure dimethyl carbonatewhilst limiting the column top temperature to 65° C. The time of meteredaddition was about 3.5 hours. The batch was subsequently heated to 200°C. again over 2 hours. Thereafter, it was stirred for 3 hours at 200° C.under normal pressure and for 5 hours at 100 mbar. An OH number of 31.3mg KOH/g and a viscosity of 33,320 mPa.s were obtained thereafter. Inorder to achieve the desired OH number, 0.395 kg adipol was subsequentlyadded. After the reaction had again proceeded for about 3 hours at 200°C. at normal pressure, and for 7 hours at 100 mbar, the OH number was52.5 mg KOH/g and the viscosity was 15,737 mPa.s.

The total reaction time was about 36 hours.

Compared with Example 5, the reaction time here was longer, the catalystrequirement was higher, and there was a greater loss of DMC.

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

What is claimed is:
 1. A process for producing an aliphaticoligocarbonate diol comprising a) reacting an aliphatic diol withdimethyl carbonate (DMC), in a transesterification, at an elevatedpressure in a reaction mixture, b) removing methanol and unreacteddimethyl carbonate under a reduced pressure, and c) completing thetransesterification and uncapping the terminal OH groups by removingmethanol and unreacted dimethyl carbonate under reduced pressureassisted by addition of an inert gas.
 2. The process of claim 1 furthercomprising adding a catalyst.
 3. The process of claim 1 furthercomprising adding the DMC to the diols in a reaction vessel after thereactor is heated and the pressure is applied.
 4. The process of claim 3comprising adding DMC slowly at first into the reactor, and laterincreasing the rate of addition to such an extent that a DMC/methanolazeotrope is distilled off.
 5. The process of claim 1 comprising addingDMC rapidly in one step.
 6. A process according to claim 1 comprisingadding up to 100% of the requested amount of DMC to the diol, heatingthe reactor, applying the pressure, refluxing all the distillate to thereactor until a defined or constant DMC content is obtained in thedistillate, distilling off the DMC/methanol mixture and adding the DMCthat is lacking compared to the required amount.
 7. The process of claim1 wherein the elevated pressure is between 1.5 and 100 bar and thetemperature is between 100 to 300° C.
 8. The process of claim 7 whereinstep b) is performed at a temperature from 160° C. to 250° C. and at apressure from 1 to 1000 mbar.
 9. The process of claim 1 comprisingintroducing the inert gas as bubbles into the reaction mixture.
 10. Theprocess of claim 1 wherein the inert gas is selected from the groupconsisting of nitrogen, noble gases, methane, ethane, propane, butane,dimethyl ethers, dry natural gas and dry hydrogen.
 11. The process ofclaim 1 wherein the inert gas is prepared from a low-boiling liquidselected from the group consisting of pentane, cyclopentane, hexane,cyclohexane, petroleum ether, diethyl ether and methyl tert-butyl ether.12. The process of claim 1 comprising removing methanol and unreacteddimethyl carbonate in a gas stream and partially recycling the gasstream to the oligocarbonate.
 13. The process of claim 1 where the totalamount of DMC is the sum of the theoretical amount of DMC to be reactedwith the aliphatic diol plus the amount of DMC distilled off during theplanned reaction time.
 14. The process of claim 1 further comprising d)modification of the molecular weight of the aliphatic oligocarbonate byadding more diol components followed by another transesterificationreaction.
 15. The process of claim 1 wherein the aliphatic diolcomprises 3 to 20 C. atoms.
 16. The process of claim 1 wherein thealiphatic diol comprises an aliphatic ester diol.
 17. The process ofclaim 16 wherein the aliphatic ester diol comprises an addition productof a diol with a lactone.
 18. The process of claim 17 wherein thelactone is caprolactone or valerolactone.
 19. The process of claim 16wherein the aliphatic ester diol comprises a condensation product of adiol with a dicarboxylic acid.
 20. The process of claim 19 wherein thedicarboxylic acid is adipic acid, glutaric acid, succinic acid, ormalonic acid.
 21. The process of claim 1 wherein the aliphatic diolcomprises a polyether polyol.
 22. The process of claim 1 wherein thealiphatic diol is polyethylene glycol, polypropylene glycol orpolybutylene glycol.
 23. The process of claim 1 wherein the aliphaticdiol is 1,6-hexanediol, 1,5-pentanediol and/or mixtures of1,6-hexanediol and caprolactone.
 24. The process of claim 16 wherein thealiphatic ester diol is formed in situ during the production of thealiphatic oligocarbonate diol.
 25. The process of claim 1, wherein themolar ratio of diol to DMC in the reaction mixture ranges between 1.01and 2.0.
 26. The process of claim 2 wherein the catalyst is a solubletransesterification catalysts.
 27. The process of claim 26 wherein thesoluble transesterification catalyst is used in concentrations up to1000 ppm.
 28. The process of claim 2 wherein the catalyst is anunsoluble transesterification catalysts.